Railroads have a strong economic incentive to maximize the length and weight of freight trains. Since the mid-1990s, various technological innovations have facilitated operation of longer and heavier trains, and railroads have made infrastructure investments to accommodate them. Recent shifts in railway operating and management strategies have placed added emphasis on long trains but have also drawn public and agency scrutiny. The advantages and disadvantages of increased train size are difficult to analyze because public data on train length and weight over time are limited. Articulated intermodal railcars, artificially short local trains, and light empty unit trains skew industry averages across all train types and mask trends over time. To provide greater insight on the average and distribution of train length and weight for different train types over time, the research team conducted a detailed analysis of Class 1 railroad annual report financial data and Surface Transportation Board waybill sample data collected for the years 1996 through 2018. Dividing traffic statistics by train type allows for a specific focus on loaded unit train length and weight distributions that isolates many factors skewing overall averages. Over the past 23 years, the average length and weight of loaded non-hazmat unit trains have steadily increased. Train size distributions indicate that unit trains exceeding 140 railcars in length have become more frequent over the past 10 years, whereas hazmat unit trains are typically smaller in size. This information can aid researchers and industry practitioners in assessing the benefits and disadvantages of operating longer trains.

铁路有强烈的经济动机来最大化货运列车的长度和重量。自 1990 年代中期以来，各种技术创新促进了更长更重列车的运行，铁路也进行了基础设施投资以适应它们。最近铁路运营和管理战略的转变更加重视长途列车，但也引起了公众和机构的审查。由于列车长度和重量随时间推移的公开数据有限，因此难以分析增加列车规模的优缺点。铰接式联运轨道车、人为缩短的慢车和轻型空单元列车会扭曲所有列车类型的行业平均值，并随着时间的推移掩盖趋势。为了更深入地了解不同列车类型的列车长度和重量随时间的平均值和分布情况，研究小组对 1996 年至 2018 年收集的 1 类铁路年度报告财务数据和地面运输委员会运单样本数据进行了详细分析. 按列车类型划分交通统计数据可以特别关注装载的单位列车长度和重量分布，从而隔离了许多影响整体平均值的因素。在过去的 23 年中，装载的非危险品单元列车的平均长度和重量稳步增加。列车大小分布表明，在过去 10 年中，长度超过 140 节轨道车的单元列车变得更加频繁，而危险品单元列车的尺寸通常较小。